The present invention relates to the field of time division multiple access (TDMA) and frequency division multiple access (FDMA) communications systems. More specifically, the present invention relates to methods and systems that improve the efficiency of transmitting packets of variable sizes through the use of new packet formatting techniques that reduce the overhead required for high data rate transmission.
Terrestrial-based and satellite-based radio communications systems are becoming more prevalent for providing radio communication services on both voice and data throughout the world. As such systems acquire more subscribers, the demands on the finite frequency bandwidth allocated to these wireless communication system increases. In addition, ever increasing data rates of the communications signals between transmitting and receiving units further increase the demand for this finite frequency bandwidth.
Radio communications systems often employ frequency division multiple access (FDMA) techniques for separating multiple transmissions over a finite frequency bandwidth. FDMA refers to the method of allocating different discrete frequency bands, or frequency channels, within the finite frequency bandwidth to different users to permit many concurrent conversations.
Radio communications systems also employ time division multiple access (TDMA) techniques for separating multiple transmissions. With TDMA, each subscriber is typically assigned a specific time slot or group of time slots in a TDMA frame. The subscriber transmits user-provided information only during each assigned time slot.
Yet another technique for separating multiple transmissions that may be employed by radio communications systems is code division multiple access (CDMA). CDMA is a spread spectrum technology that assigns a code to all speech bits, sends a scrambled transmission of the encoded speech over the air and recovers the original information FDMA, TDMA, and CDMA may be used alone or in combination.
For radio frequency (RF) TDMA communications, a time slot is often used to transmit a packet of data. Each packet includes overhead information and payload. The overhead information includes, for example, synchronizing bits, address of the destination, address of the originating device, length of packet, and so forth. The payload is user-provided data which is the object of the communications system. The payload is reassembled in response to the overhead information by the receiving equipment into the original signal. Through the use of TDMA, multiple conversations from separate subscribers can be interwoven into the TDMA frame.
There is a growing requirement to transmit data and voice on the same hardware, such as to be able to connect a cellular phone to a modem for wireless computer communications. Computer communications require a much higher data rate than voice communications. This extra data requirement has been met by providing more packets to the user. The problem with this approach is that packets optimized for low data rates such as for voice have an overhead information structure that utilizes approximately twenty-five percent of capacity of the packet in each time slot with the payload utilizing the remaining portion of the time slot. This high overhead limits is not required for high capacity links and limits the amount of data that may be carried in each time slot. This limitation reduces the efficiency of the communication link when transmitting high rate data signals.
Those skilled in the art will realize that there are many applications that require high data rates in addition to computer communications. These include video conferencing, video transmission (movies), and hi-fidelity Reallocation of capacity may be accomplished through the termination of the original communication link and the establishment of a new communication link, reallocation undesirably interferes with the voice conversation on the original circuit switched communication link. In addition to the inconvenience to the user, this reallocation activity is a highly time and resource consuming operation.
Accordingly, there is a significant need for a system and a method that can reduce the overhead for high speed data transmission and mitigate the problems associated with managing calls employing voice signals and data signals. This system should use the same hardware for both data and voice so the type of data is transparent to the user. In addition, there is a significant need for a system and a method that dynamically vary the transmission rate without the need for employing a reallocation activity.